This invention relates to froth flotation and, more particularly, to froth flotation apparatus and methods for beneficiating mineral ores, coal and the like.
Froth flotation has been used to beneficiate a variety of mineral ores and to effect separation of a wide variety of materials for many years. Froth flotation involves separation of particles in an aqueous pulp based on a difference in hydrophobicity. The pulp is aerated by contacting with fine air bubbles. The hydrophobic particles attach to the air bubbles and rise to and float on the surface of the pulp as a froth, leaving behind the hydrophilic particles.
An article entitled "Flotation Machines" in Mining Magazine, Jan. 1982, page 35, describes several different types of conventional flotation apparatus and methods for beneficiating minerals. In so-called column flotation, a conditioned pulp is introduced into the middle of the column, pressurized air is introduced into the bottom and wash water is introduced into the top. A flotation fraction containing the hydrophobic particles, usually the mineral values, overflows from the top of the column and a tailing fraction containing the hydrophilic particles, usually the gangue, is discharged from the bottom of the column by gravity or a pump. Examples of prior column flotation apparatus are disclosed in Hollingsworth, et al. U.S. Pat. No. 3,371,779, Yang U.S. Pat. No. 4,592,834 and the references cited therein.
Conventional froth flotation devices and methods typically employ a single unit for aerating the pulp and for effecting separation of the froth. Many require mechanical mixing and, therefore, are energy inefficient. Optimum phase separation requires substantially quiescent conditions, while optimum mixing of gas bubbles into a pulp requires a turbulence with a minimum relative flow velocity between the bubbles and the particles in the pulp. The overall efficiency of single unit devices is inherently limited because it is difficult to optimize the turbulent and quiescent conditions simultaneously in a single unit.